Synthetic polymer materials possess poor surface properties. Most fibers formed from synthetic polymers are not hygroscopic and have poor antistatic and soil release properties. In particular, many conventional fabrics formed from polyester and polypropylene have relatively poor hard properties. They have a slick or synthetic fabric feel. They are deficient in properties relating to hydrophilicity, in particular hygroscopic, antistatic, and soil release properties.
The prior art approaches for depositing a water soluble vinyl monomer onto a polymeric substrate may be grouped into two general categories (I) formation of a hydrophilic polymer on the surface of and within the substrate by adhesion and/or entanglement of the polymer and the substrate; (II) chemical modification of the substrate by graft polymerizing a hydrophilic monomer onto the substrate.
Examples of the first approach include U.S. Pat. Nos. 3,377,249 and 3,958,932. The method of U.S. Pat. No. 3,377,249 employs an aminoplast textile resin to effect adhesion of a synthetic acid emulsion polymer to a polymeric substrate. In the method of U.S. Pat. No. 3,958,932 the vinyl polymer is affixed to the polymeric substrate by the use of elevated temperature curing.
In U.S. Pat. No. 3,926,551 water-insoluble polymers derived from acidic vinyl monomers are formed both on the surface and within polyester fibers. In U.S. Pat. No. 3,995,998 polymers derived from both acidic and non-acidic water soluble vinyl monomers are deposited on both the surface and within the fibers forming the polymer substrate. In U.S. Pat. No. 4,238,193, an impregnated initiator is used to penetrate into the interior of a polymeric substrate fiber and to effect polymerization of a water soluble vinyl polymer both onto the surface of and within the substrate.
The second approach has been to chemically modify the polymeric substrate so as to receive the polymer from a water soluble vinyl graft polymerization. U.S. Pat. Nos. 3,088,791; 3,107,206; 3,115,418; and 3,617,457 each disclose the use of high energy radiation to modify a polymeric substrate. It is believed that the high energy radiation cleaves the bonds on the surface of a polymer to form free radicals. These free radicals participate in chemical reactions with the vinyl monomer. U.S. Pat. No. 3,088,791 irradiates a shaped organic polymer substrate at low temperatures. U.S. Pat. No. 3,107,206 irradiates a stem polymer that has been swollen with a non-polymerizable swelling agent. U.S Pat. No. 3,115,418 irradiates a polymeric substrate in the presence of oxygen. U.S. Pat. No. 3,617,457 describes irradiation of a polyester substrate and uses unique water soluble vinyl monomers.
U.S. Pat. No. 3,600,122 employs a spark discharge in a zone of free radical initiating gas to generate free radical sites on the surface of a polymeric substrate. This modified polymeric substrate is further reacted like any irradiated polymer.
U.S. Pat. No. 4,043,753 modifies a conventional polyester substrate by incorporating P-carboxycinnamic acid to replace a portion of a terephthalic acid of the polyester. The resultant polymeric substrate is a modified polyester polymer containing an unsaturated group that is susceptable to graft polymerization.
In U.S. Pat. No. 4,065,256 a composition comprising a liquid organic solvent, and a hydrophobic radical polymerization initiator is used to achieve graft polymerization onto both the surface and within a hydrophobic synthetic polymer substrate.
The above prior art approaches frequently suffer from undue expense, complex equipment requirements, and other processing shortcomings. These approaches generally can not yield a flame retardant substrate having the surface properties which we desire that will substantially withstand repeated launderings such as 20 or more launderings in a conventional washing machine.